1. Field of the Invention
This invention relates to a continuously variable transmission (CVT) chain having link plates connected by rocker joints, a rocker pin and a seat pin being received in an insertion bore in the link plate and bearing against one another along arcuate contact surfaces. More particularly the invention relates to such a chain wherein a minimum sectional area of the link plate formed between the link plate insertion bore and the outer periphery of the link plate relative to the pulley, is greater than the sectional area formed between the link plate insertion bore and the inner periphery, and the radii of curvature of the inner rolling contact surfaces of the rocker pin and seat pin are smaller than those of the outer rolling contact surfaces.
2. Prior Art
A continuously variable transmission is generally composed of a pair of pulleys mounted on a driving shaft and a driven shaft, respectively. A plurality of frictionally driven blocks, mounted on an endless chain, are entrained on said pulleys. The pulleys have opposing conical surfaces for receiving the friction blocks of the chain. The conical surfaces of one or both pulleys can be varied in their spacing to adjust the effective diameter of the pulley. When the distance between the respective conical surfaces of either or both pulleys is changed, the distance from the axis of the pulley to the contact position of the frictionally driven blocks also changes, thereby changing the effective diameter of the pulley. The resulting structure is commonly referred to as a "continuously variable transmission" or CVT, because the spacing of the conical surfaces can be adjusted to any point in a continuous range.
The present invention relates to a rocker joint pin type CVT chain, which may be a "dual row" type or a "single row" type. The blocks are mounted on link plates connected by rocker joints having two pins that bear against one another along arcuate surfaces.
FIG. 1 illustrates a single row type CVT chain of the rocker joint pin type, in which a plurality of link plates L1, L2 are endlessly connected by means of a plurality of rocker joint pins P so as to form an endless transmission chain C. A plurality of frictionally driven blocks B are mounted to the link plates, in the illustrated case surrounding the link plates in positions between the successive connecting pins P. The V-shaped inclined surfaces T, T of the blocks B frictionally engage with the conical surfaces of the pulleys (not shown) so as to form the continuously variable transmission.
In a known rocker joint chain of this type, as shown in FIG. 3a, two connecting pins Pl, P2 together form a rocker joint pin and bear against one another at points A, A'. When the chain is positioned such that the links are straight in line, the contact points A, A' of circular opposing rolling surfaces A1, A2 of the two connecting pins P1, P2 are located beneath the line N-N defined by connecting the centers of the insertion bores H, H of the rocker joint pins (i.e., internally of line N-N relative to the route of the endless chain around its pulleys). The contact points A, A' move upwardly from the center line N--N (i.e., outwardly of the chain route) with flexing of the connections of the link plates, as shown in FIG. 3b.
Consequently, with flexing of the chain, compression force is applied to the link plate inside of the center line N--N, and tensile force is applied to the link plate outside of the center line N--N, respectively.
A more detailed explanation can be made with reference to FIG. 3c. A tensile force F1 acts at the contact point A of the connecting pins at one joint; and a tensile force F2 acts at the contact point A' in the opposite direction at the other joint as the successive chain links draw one another along the chain route. Said tensile forces F1 and F2 are shown as tensile force components Ft.sub.1 and -Ft.sub.2, aligned parallel to the center line N--N; and bending moment components Fb.sub.1 and Fb.sub.2 acting inwardly as the chain passes around the pulley. Within the material of the link plate L, compression takes place inside of the center line N--N relative to the pulley; and tension takes place outside of the center line N--N due to the tensile component forces Ft.sub.1 and Ft.sub.2 as well as the bending moment forces.
A greater tensile force acts at the minimum sectional area portion D disposed between the pin insertion bore and the outer periphery of the link plate L than at the minimum sectional area portion D' between the pin insertion bore and the internal periphery of the link plate L.
Nevertheless, if the link plates L in the chain C are ordinary link plates, said two minimum sectional area portions D, D' have the same sectional areas. Hence, cracking is likely to occur sooner at the outer minimum sectional area portion D, where the forces are greater.
Furthermore, as mentioned before, the contact points A, A' of the opposing rolling contact surfaces Al and A2 of the pins P1 and P2 move from the position shown in FIG. 3a, where the links are straight in line, to a flexed position shown in FIG. 3b as result of the angular displacement of successive links with flexing of the chain C. In a conventional CVT chain, the opposing rolling contact surfaces Al and A2 are composed of arcuate surfaces having a uniform radius of curvature, i.e., defining an arc of a circle; and consequently, when the chain is in a straightened position as shown in FIG. 3a, the contact points A, A' are situated inwardly of the center line N--N by an amount E.sub.l. As a result, when the chain is straight, the tensile load is shifted partially to the inner minimum sectional area portions D', D', which causes the strength of said portions to decrease.
It would be desirable in a CVT chain of the present type to arrange the links and the connecting pins so that loads applied to the chain link plates are more nearly equalized. In this manner, the chain can withstand greater loads per unit of chain weight, and longer wear.